Phosphatizing operations carried on in water have typically provided drawbacks, including sludging and the need for a multi-step operation, to achieve dry, coated articles. In an early attempt to overcome such problems, as described in U.S. Pat. No. 2,515,934, from 1% to 7% of the commercial phosphoric acid 85% syrup was used in an organic mixture, rather than in water. Representative of these mixtures was a 50/50 blend of acetone and carbon tetrachloride. With the blend, only a few steps were needed for phosphatizing.
A different approach to overcoming the problems that are found in water-based phosphatizing systems, was taken in the process of U.S. Pat. No. 2,992,146. Therein, by means of special equipment, an aqueous phosphatizing solution was sprayed onto a metal article, while the article was being maintained in a vapor degreasing zone. The vapor degreasing zone contained the vapors from a chlorinated hydrocarbon such as trichlorethylene. The operation thereby permitted enhanced drying of panels after phosphatizing.
In subsequently developed phosphatizing operations that relied on using chlorinated solvents, the water solution for the phosphatizing was altogether eliminated. In typical operations, a metal article for phosphatizing might be dipped in a chlorinated hydrocarbon degreasing solution, then come in contact with a non-aqueous phosphatizing solution, and thereafter be returned to the chlorinated hydrocarbon degreasing solution for a final rinse operation. Such operation has been described for example in U.S. Pat. Nos. 3,100,728 and 3,197,345. As also discussed in the U.S. Pat. No. 3,197,345, it was becoming recognized that there was a water-based process, also called an "aqueous" method of phosphatizing metal articles, and on the other hand a solvent-based process, which was therein noted as the "dry" process. The latter process typically employed a solution of phosphoric acid in a chlorinated hydrocarbon solvent. Since the compositions of the U.S. Pat. No. 3,197,345 relied on chlorinated hydrocarbons, the phosphatizing method used was the "dry" process and the useful compositions were substantially water-free compositions.
As early as in the U.S. Pat. No. 2,515,934, it was recognized that the commercial phosphoric acid would introduce a small amount of water into organic phosphatizing compositions. In the U.S. Pat. No. 3,197,345 teachings, it was regarded that substantially all of the water could be distilled from the phosphatizing bath as the "dry" treatment progressed. Getting away from a dependence on phosphoric acid was also explored. From this, it was found that special organic phosphate complexes could be useful in the non-aqueous solutions. They had the advantage of providing protective coatings of enhanced corrosion resistance. This approach was taken in U.S. Pat. No. 3,249,471. Another approach to the dry process, or to the "non-aqueous" process as it was also called, and that was employed in U.S. Pat. No. 3,297,495, was the use of a high strength acid. In such patent, the acid used was preferably one of 96-100% phosphoric acid. This concentrated acid presented sludge problems, but these were overcome by employing special additives.
Other techniques, to maintain the non-aqueous phosphatizing process "dry", included the use of drying agents such as magnesium sulfate and the use of powdered metals. These concepts have been discussed in U.S. Pat. No. 3,338,754. Therein it was emphasized that small amounts of water are detrimental to the phosphate coatings obtained from the non-aqueous phosphatizing solutions. It was also early recognized in the U.S. Pat. No. 2,515,934 that the presence of water in an organic phosphatizing system could lead to the formation of two liquid phases, with attendant problems developing. Phase separation, and especially with regard to the formation of a separate aqueous phase. was discussed in U.S. Pat. No. 3,306,785. It is also noted, from the U.S. Pat. No. 3,306,785, that in developing the "dry" process with chlorinated hydrocarbons, emphasis was being placed on the commercially important trichlorethylene and perchlorethylene solvents.